4/12/2016

By Tim, John, Shane, Owen

A few refreshers  Atoms of the same element, which always have an identical number

of protons, that have different numbers of neutrons, is an isotope.  Protons and neutrons are nucleons.  AZX is an isotope, where A = mass number (protons + neutrons), Z =

atomic number (# of protons), X = elemental symbol  In a nuclear equation, the mass numbers of the reactants equal the mass numbers of the products, and the atomic numbers of the reactants equal the atomic number of the products. But the total mass for both sides will be different, due to the law of conservation of mass-energy.  The mass of a neutron = 1.008665u  The mass of a proton = 1.007276u

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What is radioactivity?  Radioactivity is a naturally occurring process in which atomic nuclei of heavy elements are __________ ___________, and emit radioactive particles.  Artificial radioactivity is a man-made process in which even light elements can emit ionizing radioactivity or particles. Also called _________ ___________, this can occur when an element is __________ by an α-particle, xrays, gamma rays, or other naturally occurring isotopes.

More about artificial radioactivity  The phenomenon of artificial radioactivity was discovered by Irene Joliet-Curie and Frederic Joliot in an experiment that awarded them the Nobel Prize in 1935. The French couple conducted an experiment that saw them ________ aluminium with α-particles to make a radioactive isotope of phosphorus. The phosphorus isotope was the first to be synthesized artificially.

+ 42He  3015P + 10n  https://www.youtube.com/watch?v=3rn339v_Q-w 

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13Al

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Nuclear Fission  Enrico Fermi discovered in the 1930’s that neutrons were the most effective at causing nuclear reactions because they do not ______ positively charged protons. We call this ______ _______ because it resembles cell division. Here is a typical fission reaction.



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0n

+ 23592U  14156Ba + 9236Kr + 310n

 Note: ( 10n) represents one neutron being released. When there is a coefficient, that is how many neutrons are being released.

Nuclear Fission  Note this equation again:

+ 23592U  14156Ba + 9236Kr + 310n  Uranium is a commonly used heavy element in nuclear fission reactions. Uranium has a much _______ mass than the fission fragments (the elemental ________), therefore a great amount of energy is released in the reaction. The products are bound _______ than the uranium nucleus, which means they’re harder to break apart, and more _______. This occurs because their nuclei have less “shielding” of electrons. 1

0n

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Nuclear Fission  So, how do we figure out how much energy was released, in MeV? U = 235.043925u, Ba = 140.9141u, Kr = 91.9250u

+ 23592U  14156Ba + 9236Kr + 310n 1) Calculate the masses for both sides 1

0n

2) Calculate the mass defect (mf – mi)

Nuclear Fission 3) Find the energy released using “E=mc2”.

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Nuclear Fission Example 2: How many atoms are released in 1.00kg of uranium-235? 1. Find the number of moles.

2. Find the number of particles from the number of moles.

Nuclear Fission  In nuclear fission reactions, extra _______ are produced, and one neutron is needed to start the reaction (note the 1 n & 31 n in the reaction). The excess neutrons produced 0 0 can go on to start other reactions, in a ______ _________ process.  FUN FACT: The first time nuclear fission was used was in the Hiroshima bombings on August 6, 1945.  When a fission bomb explodes, radioactive fission fragments are released into the atmosphere; this is called ___________ ________.

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Nuclear Fission  Radioactive fallout can be harmful to the environment and to organisms directly. The fission fragments can enter our food chain, and the results can be disastrous. α and β particles are too weak to affect us, but the stronger fission fragments can enter body through food, and affect our

cells.  Man-made fission reactions can be created and sustained by _______ ________.

Nuclear Reactors  Nuclear reactors sound convenient, but there are problems with them.  Neutrons emitted travel too fast for the reactor and they need to be slowed down to be absorbed by the uranium-235. A _________ does this – usually deuterium (21H).  Uranium-235 is hard to come by, and without enough of it, the neutrons will not be _________.  Neutrons can escape the reaction before they go to start a new fission reaction (a minimum ________ ____is needed).

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Nuclear Fusion  Nuclear fusion occurs when nuclei with smaller masses combine to make a nucleus with a larger mass. If the resultant mass is more _______ bound than the smaller masses, energy will be released.  An example of a nuclear fusion reaction is: 1 H+1 H2 H+0 e+0 v 1 1 1 1 0 1 H + 2 H  3 He 1 1 2 3 He + 3 He  4 He + 21 H 2 2 2 1  This is the reaction that occurs in the _____.

Nuclear Fusion  Nuclear fusion has its advantages over nuclear fission, because:

The total energy released is ________ There is less radioactive waste to worry about The fuel is plentiful (ex: deuterium, can be found in oceans)  Contrary to the benefits, nuclear fusion has its problems.

Fusion reactions need very high ___________ to occur in (108 K). Fusion reactions are common in stars. This is why fusion reactions can also be called _____________ _________. Fusion reactions are hard to _______ , and _______, after that high temperature is reached. This is why we do not yet have a practical nuclear fusion reactor.

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Fission, Fusion, and Energy •

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This chart demonstrates the relationship between the number of ________ in the nucleus and the ________ _________ per nucleon. 1H and 2H have ____ binding energies for ________, and 236U and 238U have ____ binding energies for _________. This is why they are the most commonly used elements for their respective reactions. ______ is the most ________ nucleus. It is the most tightly bound. This is why it has the _________ binding energy out of all the elements.

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